1. Field of the Invention
The invention pertains to a glass-to-metal seal that is suitable for hermetically sealing an electrochemical cell. The glass-to-metal seal includes a terminal pin that is roughened to enhance its high strength connection to a current collector. The problem is that while a roughened terminal pin improves the current collector connection, it detracts from the hermetic seal with the glass of the glass-to-metal seal. According to the present invention, this is overcome by passing the terminal pin through a sleeve, and the two are hermetically sealed together. The sleeve then provides the seal for the glass-to-metal seal. Cells having the sleeved/roughened terminal pin assembly are adaptable for powering a number of devices including medical applications such as a pacemaker, cardioventer defibrillator, drug pump, hearing assist device or neurostimulator.
2. Prior Art
The recent rapid development in small-sized electronic devices having various shape and size requirements necessitates comparably small-sized electrochemical cells of different designs that can be easily manufactured and used in these devices. Preferably, the electrochemical cell has a high energy density and one commonly used cell configuration is a prismatic, case-negative cell design having an intermediate cathode flanked by, and in electrical association with, opposed anode plates in contact with the casing. In conjunction with smaller size batteries, enhanced characteristics such as a novel glass-to-metal seal which is suitable for hermetically sealing an electrochemical cell as well as providing a high strength connection to a current collector, will increase the applicability of these cells to an increasing number of situations. As will be seen shortly, the prior art does not teach the use of a metal sleeve to be used in conjunction with a roughened terminal pin.
For example, the prior art in U.S. Pat. No. 5,727,313 to Paterek et al. shows a method of manufacturing vessel lid covers including conductive pin assemblies for vessel container housings. The conductive pin and vessel lid cover are plated to reduce corrosion. However, the plating is removed from the aperture receiving the pin. The assembled lid cover is then heated to fuse the fusible insulative material to the peripheral wall of the pin and the inner face of the aperture wall where the plating has been substantially removed so as to enhance the fusing step. This invention does not teach the use of a sleeve in conjunction with the conductive pin as stated in the current invention. In contrast, the invention teaches a cumbersome construction which is expensive and difficult to manufacture.
U.S. Pat. No. 6,076,017 to Taylor et al. relates to a method for forming a glass-metal hermetic seal between a metal pin and a sealing glass wherein the pin may be of molybdenum, tantalum, niobium or similar metals. The surface of the pin is subjected to a centerless grinding process for removing defects and anomalies before being circumferentially and sealingly engaged with the sealing glass. A similar method is utilized in U.S. Pat. No. 5,871,513, also to Taylor et al. This invention teaches the smoothing of a larger pin in contrast to the current invention which teaches roughening of the pin surface connected to an electrode current collector.
Also, U.S. Pat. No. 5,709,724 to Naugler et al. shows a process for fabricating a hermetic glass-to-metal seal between a conductive pin, a glass, and an outer body. The process generally includes the steps of providing a conductive pin having a layer of noble metal coated on at least a portion of its outer surface, placing glass having a softening point of less than about 650xc2x0 C. within the cavity of an outer body, inserting the coated pin into the glass, heating the components to a temperature at least equal to the softening point of the glass and less than about 700xc2x0 C., and cooling the components to solidify the glass and form a glass-to-metal seal. This invention teaches the use of a noble metal such as gold or platinum in contrast to the current invention which uses a titanium, stainless steel, or molybdenum pin. This patent also does not teach the use of a sleeve provided on the pin intermediate the sealing glass.
Finally, U.S. Pat. No. 5,658,688 to Jolson teaches a battery having an austenitic stainless steel case and a cover blank. The cover blank is provided with a small hole allowing a glass-to-metal seal to be fused to the cover blank. A metal feedthrough pin is provided and is surrounded and held in place by an insulator preferably made of Fusite 435 glass. Rather than using TA-23 or CABAL glasses which require the use of a molybdenum pin, this glass is specifically selected for its ability to fuse to a 446 stainless steel pin, thereby avoiding the difficulties associated with welding molybdenum pins. The Jolson invention differs from the current invention in its use of a stainless steel conductor pin devoid of a metal sleeve sealed to the insulating glass.
Thus, it can be seen, based on a reading of the prior art, there is a need to develop a glass-to-metal seal suitable for providing a high strength terminal connection to a current collector as well as providing a hermetic seal for an electrochemical cell. This invention will extend the applicability of the current electrochemical cells to new varieties of applications. This design is less cumbersome and more adaptable than others heretofore presented.
Roughening the terminal pin helps bolster the connection with the current collector. However, this same roughening detracts from the integrity of the glass-to-metal seal. According to the present invention, it has been discovered that the glass-to-metal seal of electrochemical cells containing a current collector and a roughened terminal pin, such as of titanium, stainless steel, or molybdenum, can be improved by positioning a sleeve or couple over that portion of the terminal pin that will be sealed to the insulating glass. The present construction includes hermetically welding the sleeve or couple at each end of the terminal pin, and forming a glass-to-metal seal incorporating the modified terminal pin, the insulating glass, and the metallic lid. The resulting assembly contains a portion of the terminal pin that has a roughened surface and is suitable for making a high strength connection to a current collector and another portion which has a relatively smooth surface which provides high strength for a glass-to-metal seal.
The foregoing and additional advantages and characterizing features of the present invention will become clearly apparent upon reading the ensuing description together with the included drawings wherein: